Researchers from the University of Surrey in UK placed twenty-two participants on a 28-hour day in a controlled environment without a natural light-dark cycle.

As a result, their sleep-wake cycle was delayed by four hours each day, until sleep occurred 12 hours out of sync with their brain clock and in the middle of what would have been their normal 'daytime'.

The team then collected blood samples to measure the participants' rhythms of gene expression.

During this disruption of sleep timing, there was a six-fold reduction in the number of genes that displayed a circadian rhythm (a rhythm with an approximately 24 hour period).

This included many regulators associated with transcription and translation, indicating widespread disruption to many biological processes.

The study also revealed which genes may be regulated by sleep-wake cycles and which are regulated by central body clocks. This finding provides new clues about sleep's function as separate from the circadian clock, researchers said.

"This research may help us to understand the negative health outcomes associated with shift work, jet lag and other conditions in which the rhythms of our genes are disrupted," senior author Professor Derk-Jan Dijk, from the Sleep Research Centre at the University of Surrey said.

"The results also imply that sleep-wake schedules can be used to influence rhythmicity in many biological processes, which may be very relevant for conditions in which our body clocks are altered, such as in ageing," Dijk said.

"Over 97 percent of rhythmic genes become out of sync with mistimed sleep and this really explains why we feel so bad during jet lag, or if we have to work irregular shifts," said co-author, Dr Simon Archer, from the School of Biosciences and Medicine at the University of Surrey.

The study is published in the journal Proceedings of the National Academy of Sciences.